Philippines landslides: A disaster waiting to happen

Death toll from the effects of Tropical Storm Tembin was made worse by human activity.

24 Dec 2017 09:41 GMT

There was an inevitability about the devastating flooding and landslides that hit the southern Philippines on Friday and Saturday.

At least 200 people are known to have died as Tropical Storm Tembin, known locally as Vinta, brought torrential rain to Mindanao, the second largest island in the country.

Tembin hit Mindanao less than a week after Tropical Storm Kai-Tak, known locally as Helen, struck Luzon and the Visayas, dropping 813mm of rain on Borongan City. This is more than one month's worth of rain.

Inevitably there were fatalities, and around 40 people lost their lives as a result of flooding and landslides.

The rainfall from Tembin was much less, at around 200mm - yet the death toll was five times greater, with many people still missing.

So what are the factors that cause a storm such as Tembin to have a seemingly disproportionate effect on the southern Philippines?

Firstly, tropical cyclones rarely hit Mindanao. Only around 10 percent of the annual rainfall here comes from these weather systems. Tropical storms and typhoons are largely confined to northern Luzon and the eastern Visayas. Mindanao is within six to nine degrees north of the equator - too close to generate the "spin" in the atmosphere to generate these cyclones.

Weather events that only rarely hit an area tend to have a much greater effect, partly because people are less prepared for them, and partly because the landscape is more vulnerable.

The second factor that makes Mindanao vulnerable is the human population. This has increased by 30 million in the last 30 years across the country, to reach 101.7 million in 2016. More people require more land and more resources.

Rising sea temperatures

Logging, much of it illegal, has been a major factor in the changing of the landscape across the island. Trees bind the soil; when they are removed, the soil is loosely bound and prone to rainfall-induced landslides.

Thirdly, the Philippines is one of the most vulnerable countries on Earth to tropical cyclones. Those cyclones are becoming "more extreme and causing greater amounts of devastation", according to several studies, including one from the University of Sheffield in 2016.

Although this study focused on wind intensities, rising sea surface temperatures across the Pacific, as a direct result of fossil fuel burning, are likely to make rainfall heavier too.

Although Mindanao is only hit by a tropical storm or typhoon once every 12 years or so, there is a significant threat of another major system approaching the island over the New Year.

Computer forecasts suggest that another major system could approach the island on New Year's Day. It is still early days, with great uncertainty, both in the storm's track and its intensity. But if it does materialise, it will be a major body-blow to the island's recovery efforts.